The principal goal of the proposed research is to investigate the chromosomal organization of the New World species Leishmania braziliensis and L. mexicana. These organisms cause a broad spectrum of human diseases and infect an extraordinary variety of vectors and reservoir hosts. The two species are each subdivided into several subspecies, based on biological and epidemiological features, yet the extent of genetic diversity within each subspecies and the relationships among them are unknown. Preliminary data obtained by pulsed field gel (PFG) electrophoresis show that stocks derived from individual geographic isolates of Leishmania have characteristic distributions of chromosome sizes (PFG karyotypes). Thus far, PFG karyotypes of different stocks have a high degree of size concordance only when stocks belong to the same subspecies. From PFG karyotyping we will determine whether chromosomal concordances occur among stocks of the same subspecies. This analysis will then be extended to the larger L. mexiciana complex. Results will give insight into the way in which genetic information is organized in Leishmania, thereby providing basic information about the biology of the organisms. The genetic diversity of the New World leishmanial species and their subspecies will be evaluated and the relationships among them clarified. PFG karyotyping can be applied to classification of isolates, and thus the results are relevant to clinical diagnosis and epidemiology.